PA needs a broad coalition of both secular and faith-based organizations opposing the legislation/amendment. Have both. Include progressive religious leaders in your campaign. That way, you address all sides. Your expertise is secular? Run with that. Have a few clergy members on your side to express why they support your campaign out of faith-based motivations. It will be beautiful.
Before you create your tees and logos, figure out who is spearheading this effort. Research the best, most voter-resonant language that you can for encapsulating your message, and let that find it's way into heading your website and creating your logo/slogan/tee shirts.
You'll need people with money to fund your efforts - research, website, logo design, tee shirts, literature, etc.
Never linger too long with the ignorant,
throw stones at their talk.
Walk only with the lovers,
the mirror of the soul gets rusty when
dipped in muddy water.